linux-kernel - RE: [tip:tracing/core] x86, bts: reenable ptrace branch trace support

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Message-ID: <928CFBE8E7CB0040959E56B4EA41A77EBBC651F4@irsmsx504.ger.corp.intel.com>
Date:	Wed, 10 Jun 2009 14:32:05 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, "mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"oleg@...hat.com" <oleg@...hat.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: RE: [tip:tracing/core] x86, bts: reenable ptrace branch trace
 support

>-----Original Message-----
>From: Peter Zijlstra [mailto:peterz@...radead.org]
>Sent: Wednesday, June 10, 2009 3:29 PM
>To: Metzger, Markus T
>Cc: Ingo Molnar; mingo@...hat.com; hpa@...or.com; linux-kernel@...r.kernel.org; tglx@...utronix.de;
>oleg@...hat.com; linux-tip-commits@...r.kernel.org
>Subject: RE: [tip:tracing/core] x86, bts: reenable ptrace branch trace support
>
>On Wed, 2009-06-10 at 14:22 +0100, Metzger, Markus T wrote:
>>
>> The Debug Store interface is completely in-kernel. It does not expose
>> anything to the outside world.
>>
>> What we expose is a ptrace interface for branch tracing.
>> That this is built on top of Debug Store is completely hidden.
>> The Debug Store interface may be changed without impacting the
>> user-visible part at any time.
>>
>> I do think that a ptrace interface makes sense since debuggers are the
>> targeted users for branch tracing.
>>
>> I don't see why we should not merge the fixes now and then rework the
>> in-kernel parts as needed for supporting PEBS.
>
>Ok, so what is all that account_locked_memory() for?

To allow debuggers (users) to decide how much memory they want to spend
on branch tracing.

regards,
markus.

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